In workholding spindle assemblies typically used in turning and grinding machines, where the work is held in a chuck attached to the nose of a spindle, the most common prior art assemblies teach that the spindle mounting bearings should be placed as close to the end of the spindle as is possible, and that the outer race of an antifriction bearing assembly should be supported by a rigid machine structure, such as a spindle housing assembly backed up by ribs or walls to give a stiff structure with a minimum of deflection at the end of the spindle. The basic teaching of these assemblies is to produce a high static stiffness by the inherent mechanical springs involved, but no thought is given to damping the structure from induced vibrations, other than the material damping properties such as are found in nodular iron.
Present day assemblies are utilizing increasingly more units made from welded steel structures, lacking cast iron damping properties, and thus the change of vibrations causing problems at the work-tool interface are becoming more acute.
Applicant has obviated the difficulties inherent in the prior art assemblies, by utilizing, in a first embodiment, a squeeze film viscous damping structure at the mounting unit which carries the spindle bearing package.
In a second embodiment, a visco-elastic damping structure is utilized at the spindle mounting unit.